Aspects of lipid metabolism were studied, using highly-developed techniques with purified mononuclear cell subpopulations, including natural killer (NK) cells and monocytes. Phospholipid and neutral lipid methylation or arachidonate metabolism were shown to be altered during NK activity, interferon treatment, and chemotaxis, or tumor promotion. Chemotaxis and superoxide generation by monocytes, evaluated by automated techniques, were correlated with changes in phospholipid metabolism. Spontaneous cytotoxicity by adherent human peripheral blood leukocytes against tumor cell lines was shown to be mediated by NK-like cells, in addition to, or instead of classical monocytes. The characteristics of the effector cells were extensively studied using well-defined monoclonal antibodies against cell surface components. Differentiation of myeloid or monocyte-like cell lines by phorbol myristate acetate (PMA) interferon (or 2'-5' oligioadenylate) and dexamethasone (or lipomodulin) was studied based on changes in morphology, antigenic expression and function in antibody-dependent cytotoxicity and ability to produce superoxide.